Electric heaters



April 26, 1960 J. MOORLLY ELECTRIC HEATERS 2 Sheets-Sheet 1 Filed Feb. 19, 1954 INVENTOR. Josspn MUmw BY HTTORNEY April 26, 1960 J. MCORLLY ELECTRIC HEATERS 2 Sheets-Sheet 2 Filed Feb. 19, 1954 INVENTOR. Joszpn M ORLLY HTTORNEY United States Patent ELECTRIC HEATERS Joseph McOrlly, Wilkinsburg, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 19, 1954, Serial No. 411,379

8 Claims. (Cl. 29155.65)

The present invention relates to methods of making sheathed electric resistance heaters and the principal object of my invention is to provide new and improved methods of this character.

In making sheathed'electric resistance heaters of the type having an electric resistor disposed within a deformable sheath which is filled with electric-insulating, heat-conductive granular refractory material, it is necessar after the filling operation, to clo'se'the ends of the sheath by, some means toprevent loss of the refractory material during subsequent operations.

In the past, the ends of the sheath have been closed by an operation known in the trade as end-packing and such operation, comprises the placing of one or more pellets formed of a brittle, dielectric material in a respective end of the sheath and crushing such pellets by repeated blows delivered through a respective open end of the sheath until a tightly packed wad of dielectric material had been formed. Following end-packing each end of the sheath, the portion of the sheath intermediate the ends was compressed as by being pressed between dies in a press or the like, to partially compact the refractory material about the resistor so as to prevent it from shifting from its normal position wherein it is spaced from the wall of the sheath. After partially compacting the refractory about the resistor, it was possible to form the sheath, by bending or the like, to the desirable shape after which the previously mentioned intermediate portion of the sheath was further pressed, as between dies or the like, the further compact the refractory material about the resistor to obtain the necessary density for maximum heat transfer of the refractory material.

The above described prior art method of making sheathed electric heaters has been more or less satisfactory; however, this method has been quite expensive and a considerable portion of this expense has been the end-packing operation and the initial, or partial, compacting operation. Accordingly, it is an object of my invention to simplify and reduce the cost of producing electric heaters of the character described. The means by which this and other objects are achieved will become.

apparent from a study of the following description and from the drawings appended hereto.

In the drawings accompanying this specification .and forming apart ofthis application there are shown, for purpose0f'illustration, embodiments which my invention may assume, and in these drawings:

Figure 1 is a broken, longitudinal sectional view of an" electric heater illustrating one step of my improved method of manufacturing the same,

Figure 2 is a view similar to Figure l but illustrating the heater after another step,

Figure 3 is a reduced size, diagrammatic'view of still heater illustrating its appearance following the step shown Patented Apr. 26, 1960 Figure 5 is a sectional view generally corresponding to the line 5--5 of Figure 4,

Figure 6 is a broken elevational view of the lectric heater illustrating another step in my improved method,

Figure 7 is a view of the heater shown in Figure. 6 but in longitudinal section,

Figure 8 is a sectional view generally corresponding to the line 88 of Figure 6,

Figure 9 is a plan view of another type of heater constructed in accordance with my invention,

Figure 10 is a fragmentary view generally corresponding to the line 10-10 of Figure 9, and

Figure 11 is a broken, fragmentary elevational view illustrating a step in the formation of the heater shown in Figure 9. i

In the practice of my improved method of manufacturinsulating, heat-conductive refractory material 13 which, i

in the presently disclosed embodiment, is granular in form. Any suitable means may be employed to fill the sheath 12; for example, any suitable commercially available filling machine may be utilized and since such machines are well-known in the art, a detailed description thereof is believed to be unnecessary.

During the filling operation as herein disclosed, the sheath 12 is adapted to be positioned generally vertically and the refractory material 13 is introduced into the uppermost end of the sheath and allowed to gravitate down to fill the sheath, the filling being accompanied by vibration ofthe sheath so as to compact the granular material to a certain degree. At the present time it is preferable to close the bottom of the sheath by means of a plug 14 which is of a size to closely fit within the sheath 12 and which is apertured to pass the lower terminal pin 11 with a minimum of clearance.

The plug 14 may be formed of any suitable material which possesses the necessary degree of plasticity; for example, plugs of rubber, plastic, crushable ceramic bodies,

and an igneous mineral material have variously been successfully employed depending upon ultimate use of the heater and also depending upon the nature of certain following manufacturing processes, such as annealing. During filling, the plug 14 may be held within the sheath by frictional engagement therewith or by any other suitable means such as by engagement with an abutment which may form a part of the filling machine.

After the sheath 12 has been filled with refractory material, a plug 15, similar in all respects to plug 14, may be positioned in the upper end of the sheath (see Figure 2). It will be apreciated that the sheath will not be completely filled with the refractory material but that sufii cient space will be provided for receiving the plug 15.

The filling operation, up to this point, is generally in accordance with methods now practiced. However, despite vibration and other compacting aidsduring thefilling operation, it has been found that the refractory material 13 is not compacted sufficiently to restrain the resistor 10 against lateral movement and that the resistor Forexample, in some instances when the heating elements are filled by prior art methods and when the elements are stored for any length of time with their axes generally horizontal, it has been found that the granu- I lar material is not sufficiently compacted and that the 4 force of gravity alone is sufiicient to cause lateral shifting of the resistor toward the inside wall of its sheath, and such element will therefore be subject to undesirable. grounding between the resistor and the sheath. Since the heatingelements are normally tested at a' later stage of manufacture for electrical shorts, it will be appreciatedthat much loss in manufacturing operations may result.

In any event, further handling or storage of the elements made in the prior art manner must'be carefully carried out and held to a minimum to prevent excessive lateral shifting of the resistor, and in mass production methods this is not feasible.

In my improved method of forming heating elements, the latter are taken from the filling operation and are immediately subjected to a lateral compression in a manner to laterally compact the refractorysubstantially equally-from all radial directions, the compaction being carried out to preferably change the cross-sectional'size of the sheath without materially changing its crosssectional circumference.

Rolling of the sheath to the different cross-sectional size is preferable since it lends itself well to high production methods. Thus, for example, a sheath, after it is filled and has both plugs in place, may be removed operator, and the finished rolled elements may be caughtin containers positioned at the exit side of the rolls.

In the manufacture of sheathed electric heaters of the general type herein disclosed, it has been found that an initial reduction in cross-sectional area of about ten per-' cent produces satisfactory results, although such reduction may vary in accordance with conditions. In order to effect the initial. reduction, and in the case of an initially round sheath, I prefer to laterally compress the sheath, preferably for its full extent, to a polygonal cross-section and at the present time a hexagonal shape is preferred, the reduction being controlled so that the perimeter of the hexagonal cross-section is substantially equal to the perimeter of the initially round cross-section. In this manner, compacting force may be applied radially of the sheath in substantially equal amounts completely about the cross-section of the sheath so that compaction of the refractory material does not cause any material lateral shifting of the resistor. By way of example, but by no means as a limitation, I may use an initially round cross-section tube having an outside diameter of about .3125 inch and form it in the manner hereinbefore described to a hexagonal shape having substantially equal sides each about .0521 inch in length.

Compressing substantially the full length of the sheath, as above described, not only results in satisfactory compaction of the refractory material without harmful transverse shifting of the resistor but also results in simultaneous securement of the plugs 14 and 15 within the ends of the sheath so that heater may be stored or subsequently handled or operated upon without the care re quired, of heating elements made'in the prior. art manner.

As'before mentioned, the heating elements after filling; may be laterally compressed either by diesor by rolls.

When the elements arecompressedbetween dies, little elongation of'the elementis effected1unles81the compres sion isconsiderably greater than herein contemplated. However, rolling of the element is preferred since rolling lends itself well. to mass, production methods and requires a' minimum of labor.

In the rolling of heating elements, the rolls should preferably be made relatively large in diameter as compared with the cross-section size of the heater. In the drawings, the rolls 16-16 are merly shown for purposes of..disc1osure. and. to conserve. drawing space. such.

rolls are not shown as large as they normally would be for the heating element shown about to enter the bight of such rolls. In Figure 3, the vector y represents the compacting force of the roll 16 and the vector x represents the force exerted against the sheath when the latter enters the bight of the rolls, the resulting vector v representing the forcetending to elongate the element. Accordingly, the rolls 16-16 should be made of relatively large diameter so that the angle z between the arrows x and y is so small as to form a negligible force 1/ tendingto elongate the element.

After the refractory material in the heating element has been compacted by hex rolling, as before described, the element, or any selected part or parts'of its length may be subsequently further subjected to compression, such as by swaging or compression between dies, to further compact the refractory material. It has been found that when swaging is resorted to for final density of the refractory material, better control of the swaged length can be realized when swaging is preceded'by'rolling" to polygonal shape since less sheath growth results.

Compressing substantially the full length of'the sheath, as pointed out above, simultaneously secures plugs 14 and 15 in position and partially compacts the refractory ma.-

terial within the sheath to hold the resistor in position. Accordingly, I eliminate the expensive end-packing operation heretoforeemployed. Another advantage of form-- ing the-sheath to a polygonal and more particularly to a hexagonal shape is that such a shape provides a transverse axis (x-x in Figure 5) about which the sheath may be bent in the event a coiled or otherwise formed element is to be made directly from the hex cross-sectional shape. Still another advantage of forming the sheath to' ahexagonal shape is that the plugs 14, 15 are thereby firmly clamped within the sheath but without stressing such plugs excessively. It will be appreciated that in the event plugs having relatively limited properties of plasticity are employed, the stresses to which they are subjected must be kept within certain well-defined limits.

As diagrammatically shown in Figure 3, a pair of rolls 16 form a pass through which the heater shown in Figure.

2 is adapted to be fed. The rolls 16 will have their working faces formed to shape the sheath to the hexagonal configuration described, and while I have shown only two rolls 16 forming a single pass, I may, if desired, employ a plurality of rolls forming a plurality of passes.

After the heater has been formed as shown in Figures 4 and 5, it may be bent to a shape applicable to its future use. For example, it may be formed to a spiral shape, a hairpin shape, or any other shape required.

If a straight heater is to be formed, the sheath 12 adjacent the coiled resistor 10 will be further compressed following the initial compression operation hereinabove. disclosed to further compact the refractory material about the resistor (see Figures 6 and 7). Any suitable means may be employed to compress this portion of the sheath without disturbing the ends thereof wherein the bushings 14, 15 are disposed. For example, the sheath may be placed between the dies of a press, the dies being proportioned to exert pressure upon only the intermediate portion of the sheath, or such compression may be made by use of swaging dies;

As herein disclosed, the il'ltGIIl'lBdiBlE.POYfiOIIIOf'thBT sheath 12 is compressed to a-roundconfiguration-(see es pecially Figure 8);-however, it is to be understood that the intermediate portionv of the sheath may be; compressed to any other suitable configuration, for example, to a triangular configuration if desired.

In forming the spiraled heater. shown in 'Figure 9, the steps illustrated in Figures 1 through 4 will be. employed. However, after the heater has been formed as shownin Figure 4, portions 17 ofthe heater (see Figure. 11) will.

preferably be compressed to a round cross-sectionin a manner similar to that employed in forming the heater. shown in Figure 6. As illustrated, only the portions. 17

near the ends of the heater will be so compressed, the extreme ends 18 of the heater and the portion 19 intermediate the portions 17 preferably remaining in their form shown in Figure 4.

It is to be understood that if a spiraled element such as shown in Figure 9 is to be formed, the resistor 10 will be preferably limited in extent to the extent of the portion 19 (Figure 11) and each terminal pin 11 will accordingly extend into the sheath 12 beyonda respective portion 17 and into the portion 19.

After the heater has been formed as shown in Figure 11, the portion 19 of the heater will be formed to a spiral configuration (Figure 9) and the portions 17 will be bent to provide terminal ends which extend from the spiral as shown. It is preferable to compress the sheath portions 17 prior to bending such portions or spiralling of the intermediate portion 19 since such compression is more readily accomplished with the heating element straight, and also since such compression will firmly hold the terminal pins centered and obviate the possibility of the terminal pins shifting laterally toward the inner wall of the sheath during bending operations.

Following the operation of forming the heater to the spiral configuration disclosed, the spiraled portion 19 of the heater will be compressed to further compact the refractory material about the resistor to obtain the necessary density. At the present time, the portion 19 is placed between dies and side-pressed to a triangular or heart-shaped configuration (see Figure 10); however, it will be appreciated that the portion 19 could be compressed to a round, oval or any other desired shape.

Under certain circumstances it may be desirable to eliminate the operation of compressing the portions 17 of the sheath and to coil the portion 19 of the heater after it has been formed as shown in Figure 4.

While I have illustrated and described the formation of only two types of heaters, a straight heater and a convoluted or spiral heater, it will be appreciated that any other suitably shaped heater may be formed if desired.

In view of the foregoing it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it will also be ap parent to those skilled in-the art that the embodiments herein described may be variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described, hence it will be appreciated that therein disclosed embodiments are illustrative only, and that my invention is not limited thereto.

I claim:

1. In the manufacture of tubular, metallic sheathed electric heating elements, the method which comprises disposing within a round cross-sectioned, elongated metal tube an electric resistor and granular electric-insulating material in relation whereby such material insulates the resistor from the tube, confining said material within said tube by use of plugs within the terminal ends of the latter, exerting lateral pressure on one terminal end of the tube at a plurality of equally spaced places thereabout to reduce its internal size and compact the insulating material therein by changing the transverse shape of the tube while maintaining its peripheral size substantially unchanged to minimize tube elongation and work-hardening thereof, and progressively advancing said pressure along said tube from the latters one terminal end to its opposite terminal end.

2. The method of claim 1 wherein the lateral pressure is applied by a rolling operation.

3. The method of claim 1 which includes anchoring said plugs by lateral pressure applied to respective terminal ends.

4. The method of claim 1 which includes anchoring said plugs by the same lateral pressure which changes the transverse shape of said tube.

5. In the manufacture of tubular, metallic sheathed electric heating elements, the method which comprises disposing Within a round cross-sectioned, elongated metal tube an electric resistor and granular electric-insulating material in relation whereby such material insulates the resistor from the tube, confining said material within said tube by use of plugs within the terminal ends of the latter, exerting lateral pressure on one terminal end of the tube at a plurality of equally spaced places thereabout to reduce its internal size and compact the insulating material therein by changing the transverse shape of the tube while maintaining its peripheral size substantially unchanged to minimize tube elongation and workhardening thereof, progressively advancing said pressure along said tube from the latters one terminal end to its opposite terminal end, and exerting lateral pressure on the tube intermediate its ends to further reduce the internal size of the intermediate tube portion and further compact the insulating material thereat.

6. In the manufacture of tubular, metallic sheathed electric heating elements, the method which comprises disposing within a round cross-sectioned, elongated metal tube an electric resistor and granular electric-insulating material in relation whereby such material insulates the resistor from the tube, confining said material within said tube by use of plugs within the terminal ends of the latter, pressing one terminal end of the tube to a hexagonal configuration to reduce its internal size and compact the insulating material therein while maintaining its peripheral size substantially unchanged to minimize tube elongation and work-hardening thereof, progressively advancing the'hexagonal configuration of the tube from the latters one terminal end to its opposite terminal end, and exerting lateral pressure on the tube intermediate its ends to further reduce the internal size of the intermediate tube portion and further compact the insulating material thereat.

7. The method of claim 6 wherein the hexagonal configuration is produced by a rolling operation.

8. The method of claim 3 and including forming the intermediate tube portion to generally triangular crosssection by the further reduction resulting from the last mentioned application of lateral pressure.

References Cited in the file of this patent UNITED STATES PATENTS 1,669,385 Wiegand et a1. May 8, 1928 1,963,057 Wilcox June 12, 1934 2,091,839 Tangeman Aug. 31, 1937 2,130,715 Coupler Sept. 30, 1938 2,375,058 Wiegand May 1, 1945 2,538,808 Swiss Ian. 23, 1951 

